In this months ‘My Automated Home’ feature, Nigel Giddings shows us his ingenious set-up that grabs a 3G signal from one corner of his rural idyll, beams it 300 meters back to his home and redistributes it to the family. If you’re in the countryside and conventional ADSL or cable broadband is not available, then there’s still hope. Read on for all the photos and details.
My family and I recently decided to have a change of lifestyle, having lived all our lives within 20 miles of London we decided to ‘emigrate’ to Cornwall. We decided to move to a rural part of the county, no town or village life for us. Since April we have been living on Bodmin Moor, many of you will have heard of Bodmin Moor and the Beast that is supposed to live here, in fact we are a few miles from the hamlet of Bolventor which is the location of Jamaica Inn made famous by Dauphine du Maurier in her book of the same name.
The downside of such a great location is that technology has passed it by. We do have mains electricity and water, although some of our neighbours don’t even have that… We do have telephone service although the cable length is twice that which can support ADSL, I have also been told that even dial-up struggles due to attenuation on the line.
A view from the ‘back garden’
Off course I checked all this out before we moved, but it didn’t stop us. With enough effort most things can be overcome and the location was too good to pass by. Options for Broadband included Satellite or ADSL delivered to another location and extended by point to point WiFi. Mobile (wireless) Broadband wasn’t an option because the only coverage locally was provided by Vodafone and only as GPRS (2.5G).
Using 2.5G Data – Having moved house in April 2010 and because much of my time was being taken up with work in the Middle East I had made no progress with a broadband solution and the family were reduced to using 2.5G through USB dongles and GSM handsets which was much less than adequate. E-mail would dribble in and browsing was very hit and miss, not ideal when your trying to start a new business. However, even at these low data rates (circa 50Kbs) the family were typically using between 4 and 5GBs of data a month.
A quick solution would have been to install a satellite link. However, at £1,000 install and a monthly fee of £30 plus it was not a cheap option. This may have been the solution but even at £30 a month you are capped at 3GB download which would not meet our needs based on our current usage when restricted to 2.5G. Previously when we had ‘Broadband’ via ADSL we would consume 40 ~ 50GB a month.
A glimmer of hope – A recent visit by a friend reopened the discussion on what solution to use. My friend and his wife use a number of mobile devices with different mobile networks, in particular his wife uses a ‘3’ SIM for data. My friend, who was more optimistic about mobile coverage in Cornwall than me suggested we take a walk around to see what was available. I was somewhat surprised to see that we had 3G coverage at the edge of our site on a piece of high ground. Especially when having reviewed the serving sites on the OFCOM website sometime earlier it indicated all the local sites used by the various operators were 2G only!
Coverage plot showing coverage of the ‘3’ network locally. The red star shows where we were able to get a signal. I have to congratulate ‘3’ on their prediction s/w. The Blue star shows were I live
A bit of further testing showed that it was possible to receive a 3.5G signal (HSDPA) with a theoretical maximum download of 7.2Mbs. Happy Days!
What to do now? – So having established that ‘mobile broadband’ was available in the area there was now the issue of how to connect it back to the house. Although the signal was still on our site it was 300 metres from the house. The limit for Ethernet over CAT5(e) is 100 metres. I did run into this limit once before at my previous house but was able to install a simple 100M switch midway to act as a repeater, I was lucky as I had a garden shed with power to house the switch half way along the route. This was installed as a temporary solution (it lasted a couple of years and I cut the cable twice accidently during that time while cutting the grass!). The link did suffer from a couple of lightning strikes in that time and any ‘permanent’ solution would need protection, either lightning arrestors or even an upgrade to fibre. This time it was 300 metres with no power options along the route and while I don’t cut the grass, the sheep do that, trying to protect a delicate cable over that distance through rough ground with roaming ruminants would be difficult.
With the advent of ‘Mobile Broadband’ a few interesting devices have also been developed. One is the MiFi, a 3G Modem back to back with a WAP (WiFi Wireless Access Point) but these are meant for personal use with self contained batteries and low power outputs. Another option is a 3G gateway, the Huawei B970 has a 3G transceiver with modem compatible with HSDPA (3.5G theoretical maximum download of 7.2Mbps), a 4 port 10/100 Ethernet switch, and built in WiFi. You can also connect an analogue telephone line and it is powered by a USB lead.
The obvious thing to do was to use a 3G gateway at the hilltop and then have a point to point WiFi link back to the house. Power would initially be supplied by a leisure battery through a USB converter until a more suitable 230V supply could be provided. (That is another story…)
The Huawei B970 is not designed for external use so needs to be protected from the weather. Because the speed archived on the 3G connection is dependant on signal strength it also made sense to mount the Gateway as high as possible in what was a marginal signal area. It was therefore decided to mount the unit at the top of a 20ft pole.
The Gateway located in a box on top of the 20ft pole on the ‘Hilltop’ looking towards
the house 300M in the distance. A power lead is taped to the pole and connected
to an 85AH Leisure Battery on the ground
A view inside the box with a cigarette lighter 12VDC – USB 5V converter
Bridging the 300 metre divide – With the Gateway 20ft in the air, on a hilltop, in a weather proof box (plastic) and pointing roughly towards the house, with almost clear line of site, there was not enough WiFi signal to reach the house some 300 metres away. The free space loss for 2.4GHz over 300 metres is approx 90dB.
The system levels can be assumed to be:
- Gateway Output power 20dBm
- Free space loss -90dB
- RESULT -70dBm
- Rx Sensitivity -80dBm
picture interfere with the LoS (Line of Sight) slightly
By adding all these figures together we get a theoretical ‘margin’ of 10dB in our favour, that is to say the receiver gets -70dBm when it only requires -80dBm. However in the real world the link did not work without an additional high gain antenna. This is probably because the WiFi output of the Gateway would be nearer 14 or 16 dBm, the losses caused by encasing the gateway in a plastic box (no external antenna) take off another 2 or 3dB and the effect of some trees in the line of sight…. As you see things quickly work against you.
Unfortunately the Gateway does not have provision for an external WiFi antenna (although you can connect an external 3G antenna). So the only way to get more gain into the system was to install a directional WiFi antenna at the house.
There are many and various suppliers of WiFi high gain antennas and I was cautious about some of the quoted gain figures. Having researched the losses and obtained some idea of output powers, receiver sensitivity, path loss, rain fade, fiddle factor, I guesstimated that I needed something like 10dB or more additional gain. dB (decibels) is a logarithmic scale and 10dB gain actually means a multiplication of 10 times. To put it another way, if you put 100mW into the antenna an antenna with 10dB gain will radiate 100mW x 10 = 1,000mW (1 Watt). Note the UK power limit is 100mW (20dBm) and refers to radiated power out of the antenna including any antenna system gain.
I selected a seller from e-bay offering a flat panel antenna with a quoted gain of16dBi for £25 inc P&P, that’s potentially 4W EIRP (effective isotropic radiated power) for 100mW input… or to put it another way a gain of 40 times. Even if the antenna is 16dBi you will have additional losses due to connectors and cable (as much as 2 ~3 dB). The supplied cable was 500mm which is good, you see some antennas for sale with cables of several metres and any gain in the antenna could be lost in low quality coax. You are better off keeping the antenna tails as short as possible even if this means installing the transceiver outside. I have no way of accurately measuring the gains and losses in the system so it is impossible to confirm any of these figures.
A closer view of the WiFi client showing the flat panel antenna more clearly
The WAP being used previously before it was installed as the WiFi Client in the waterproof box.
The Antenna in the picture can be removed and the external antenna connected
to the RP-SMA (Reverse SMA) connector
The WAP used at the house can be configured as client mode and is configured the same way you would configure WiFi in a laptop. The link which operates in the 2.4 GHz band has been set to a channel so as not to interfere with the house WiFi signal. Although there are 11 channels in the 2.4GHz band they overlap and so it is recommended to use channels 1, 5 and 11 to prevent co-channel interference. We are ‘lucky’ here in that there is no other WiFi in the area so we manage our own frequency reuse plan, in a built up area it is more of a free for all. It is possible to use 5GHz instead, which is a much quieter band, but equipment for this is not as readily available so I am going for the KISS principle.
Configuring the system – This is relatively easy, if you have configured WiFi in your own house this follows the same principles. There are a couple of things to consider as this is a point to point link and not the normal point to multi-point as used in a typical WiFi install.
Security. This is always an issue. A minimum security requirement is to use some form of encryption, most devices support WPA with a PSK (Pre Shared Key). Many devices allow MAC filtering; this restricts which devices can connect to only devices that have been listed in the filter, in this case the equipment at the other end of the link can establish a connection. SSID Broadcasting, this can be turned off so that your equipment does not broadcast its presence and therefore other equipment does not attempt to connect and it does not show up if people scan (War Drive) while in the area of coverage.
Antenna Gain. It is better not to over egg the power in the system. What you see as a strong stable signal is interference for others and could create an escalation of power output in the area serving to raise the ‘noise floor’ working against everyone. Another disadvantage of high power is that the number of people in range of your system increases and could raise the threat of a security breach.
IP Settings. As you can see from the diagram below the link uses the private 192.168.x.x ip range and is different from the main LAN IP range (which for me is just an extension of the WAN). My LAN is protected by an ISA server Firewall. Placing a hardware router here would replace the ADSL Modem/Router in an ADSL network and would provide similar protection. The 3G router can provide DHCP but this is normally off as devices have static addresses and all IP traffic should originate on the LAN and be routed via the firewall. It does mean, however, if you configure a WiFi device with the 3G gateway settings (and you configure the MAC filtering) that a direct connection can be made to the 3G gateway for testing and temporary internet connections.
The results – The link has been in service for just over a week now. The improvement in Internet access is enormous. Using 2.5G (Narrowband) meant that we experienced many timeouts while waiting for pages to load (Facebook was almost always unusable) and downloading updates / applications and even keeping the antivirus database up to date was a problem.
We now have access to services like YouTube, BBC iPlayer and other streaming type services, something that just didn’t work before. I am still watching how much data we consume as the Mobile Broadband package we have is limited to 15GB a month and we are now averaging 400MB a day which will increase significantly if we use these multimedia type services.
As you can see from the Speedtest.net results we are getting a healthy upload and download speeds although the latency figures are much higher than you would expect to get from an equivalent ‘Wired’ service. These results have varied through the days of the week but as the connection is new I haven’t identified the patterns as yet.
Speedtest.net test carried out on a Sunday afternoon
The connection is not without its problems and I have had to remotely reset the 3G gateway three times in 2 days. Either side of this period the link was solid and the problems appear to be related to the 3G network side of things although I cannot prove this. (Latest news, 34 hours up with no issues)
The Hilltop installation uses a 12V 85AH leisure battery fed through a Car Cigarette lighter – USB adaptor which provides the 5VDC that runs the unit. Measurements of the current draw were taken to try to calculate the life of a battery on Full charge.
Measurement of the Current drawn by the 3G Gateway (216.7mA)
Using 250mW for easier maths and assuming a battery voltage of 12.5V this translates to just over 3W (3.125W). Using this value we can assume that at the 5V USB converter we are drawing 625mA (3.125/5), by overstating the current we also allow for inefficiency in the voltage converter. This is important as the USB convertors come in various sizes, those that are not rated appear to be 400mA typically which is not enough in this case! I know this because the first one I used caused erratic behaviour of the gateway. It would do a factory reset if the unit was put under load (connected to 3G signal). The regulator installed now is rated at 2000mA and the unit no longer resets.
Assuming 250mA (allowing for variations as the battery voltage drops over time) that would give 340 hours (0.25A x 85AH) but again I am sure this will not be reached. There are 168 hours in a week so it would seem prudent / reasonable to swap the battery with a fully charged replacement once a week.
The next steps – From an ongoing maintenance point of view the first thing is to provide a mains 230 VAC supply. The battery may still remain in case of power failures but depends on being able to source a suitable charger that doesn’t slowly cook the battery.
Although the 3G signal seems good at the Gateway the Gateway web interface occasionally reports a drop in throughput to 384Kbps (from 7.2Mbps D/L) on the 3G interface. This is probably due to being on the edge of HSDPA range although the gateway does not report signal strength so this is difficult to correlate. I am considering installing a directional 3G antenna to increase signal strength of the 3G signal and reduce potential interference from other 3G sites on the same channels which may be interfering with the signal (The gateway is located on a high spot).
Now that we have the ability to use much more than the Data Allowance we have been given (15GB per month for £15.99) I will be looking at how I can increase the Data Allowance, I would be happy to do this in increments of £15.99 per 15GB but that is not possible with a single SIM at this time.
I do have a two-section lattice tower which I intend to install with the 20ft pole on top, this should give me 60ft AGL (above Ground Level) and will enable me to look at how I can get a faster service delivered nearby (BT infinity?) and bring that back to the site.
Over the next year I will be providing WiFi over the entire 50 acre site to work in with our plans to provide intranet access that enables paying visitors to interact with the animal exhibits we are currently planning to build, watch this space….